Rigid foam compositions and methods employing alkyl alkanoates as a blowing agent

ABSTRACT

A method for producing a rigid, closed-cell polyurethane foam having a free-rise density of from about 1.3 lbs/ft.3 to about 4 lbs/ft.3 and exhibiting a shrinkage of less than 10%, comprises mixing together an isocyanate, at least one alkyl alkanoate blowing agent and at least one polyol having a hydroxyl number of from about 150 to about 800 and being selected from the group consisting of polyalkoxylated amines, polyalkoxylated ethers, and polyester polyols, to form a reaction mixture that is curable to produce such foam.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to rigid polyurethane foams, and moreparticularly to the preparation of such foams with alkyl alkanoates,preferably, methyl formate as the sole or primary blowing agent.

2. Description of the Prior Art

Rigid polyurethane foams are useful in a wide range of applications,including applications for insulation in refrigeration systems,structural applications and flotation applications, as in boats, buoys,docks and other flotation devices. In such applications, not only thedensity and closed cell content of the foam, but also the ability of thefoam to retain its dimensional stability in adverse conditions arecritical. In fact, in flotation applications, the United Statesgovernment has specified rigorous test methods and standards for suchcharacteristics of foams in relevant applications associated with theUnited States Coast Guard. See, for example, 33 CFR § 183.114 and thetest methods set forth in ASTM D2126.

Conventionally, processes employing two components or three componentshave been used to prepare rigid foams. One component, generally referredto as component A (or A-side), comprises isocyanate. Frequently,component A also comprises a surfactant and a blowing agent. The secondcomponent, known generally as component B (or B-side), comprises any ofvarious polyols, particularly polyether and/or polyester polyols.Component B may also comprise a surfactant, a catalyst package and ablowing agent, any or all of which may reside solely in component B.Alternatively, any or all of such ingredients may be introduced to thereaction mixture in a third stream or in both component B and a thirdstream. If an excess of isocyanate is employed, modifiedpolyisocyanurate foams may be formed. The foams produced by thesestandard methods commonly have a density in the range of from about 1lb./ft.³ to about 4 lb./ft.³, have a closed cell content on the order ofabout 85% and have low friability characteristics.

Ordinarily, the polyols are poly-functional; that is, the polyolmolecule has two or more branches, which provide linking sites forcross-polymerization. Historically, the blowing agent is or at leastincludes one or more chlorofluorocarbon (CFC), often in combination withwater. However, CFCs have been the subject of environmental concern inview of the deleterious effects that they have been reported to have onthe earth's ozone layer. Therefore, it is desirable to avoid use of CFCsand the industry for many years has been searching for viablealternative blowing agents suitable for preparation of rigidpolyurethane foam.

Certain processes that employ HCFCs in place of CFCs have been reported.For example, U.S. Pat. Nos. 5,032,623, 5,194,175 and 5,274,007 describea process by which an HCFC, monochlorodifluoromethane (CHClF₂), canreplace traditional CFCs in the preparation of rigid foams. However,even HCFCs, while markedly better than CFCs in terms of deleteriousenvironmental effects, still are associated with environmental risks andso it is optimal if even their use is avoided.

Attempts at the use of alkyl alkanoates, including methyl formate, as analternative blowing agent have been reported, but those attempts havebeen unsuccessful in that the foams that have been produced with methylformate as the primary or sole (other than, perhaps, water) blowingagent are unsatisfactory. In particular, it has been found that suchfoams have a foam shrinkage of more than 10% and so demonstrate poordimensional stability. See, for example, U.S. Pat. No. 5,283,003 toChen. Thus, use of methyl formate as a blowing agent has been reportedto produce a dimensionally stable foam only when used in combinationwith a substantial amount of one or more additional blowing agents suchas organic or even hydrocarbon or traditional CFC or HFC types ofblowing agents. According to the U.S. Pat. No. 5,283,003 to Chen,methylene chloride and/or five-carbon hydrocarbons (e.g., n-pentane,isopentane, and/or cyclopentane) blowing agents must make up at leastabout 20% by weight of the total blowing agent combination. U.S. Pat.No. 5,883,146 to Tucker describes the use of formic acid (or a saltthereof) as a blowing agent, but only in combination with a C₁ to C₄hydrofluorocarbon. Although the patent to Tucker does not define thenecessary relative proportions of the formic acid (or salt thereof) andthe hydrofluorocarbon, the exemplification show that thehydrofluorocarbon must make up at least about half the blowing agentcombination by weight.

Accordingly, the rigid foam industry is still searching for methods andcompositions that would enable methyl formate or a related compound tobe used as a blowing agent that can produce a rigid foam that meets thestandards for such foams, but without the need for other organic blowingagents. Such standards include not only those relating to density andclosed cell content, but also those relating to dimensional stability(resistance to shrinkage) as well.

SUMMARY OF THE INVENTION

Briefly, therefore, the present invention is directed to a novel methodfor producing a rigid, closed-cell polyurethane foam having a free-risedensity of from about 1.3 lbs./ft.³ to about 4 lbs./ft.³ and exhibitinga shrinkage of less than 10%.

According to the method, an isocyanate, a blend of polyols of hydroxylnumbers of from about 150 to about 800, and at least one alkyl alkanoate(and/or derivative and/or precursor thereof) blowing agent are mixedtogether to form a reaction mixture that produces the foam. The blend ofpolyols in which at least 50% by weight is made up of at least onepolyol having a hydroxyl number of from about 150 to about 800 and beingselected from the group consisting of polyalkoxylated amines,polyalkoxylated ethers, and polyester polyols.

The present invention is also directed to a novel reaction mixture thatcan react to form a rigid, closed-cell polyurethane foam having afree-rise density of from about 1.3 lbs./ft.³ to about 4 lbs./ft.³ andexhibiting a shrinkage of less than 10%. The reaction mixture comprisesthe isocyanate, the blend of polyols, and at least one alkyl alkanoate(and/or derivative and/or precursor thereof) blowing agent describedabove.

The present invention is also directed to a novel rigid, closed-cellpolyurethane foam having a free-rise density of from about 1.3 lbs./ft.³to about 4 lbs./ft.³ and exhibiting a shrinkage of less than 10%,comprising cells containing gas, at least about 40% by weight of the gasbeing a combination of at least one alkyl alkanoate and carbon dioxide.

Among the several advantages found to be achieved by the presentinvention, therefore, may be noted the provision of a method forpreparation of rigid foam of high dimensional stability in whichstandard CFC, HCFC, HFC and hydrocarbon blowing agents are not needed;the provision of such method in which no standard organic blowing agentother than an alkyl alkanoate is needed; the provision of a reactionmixture that does not include CFC, HCFC, HFC or hydrocarbon blowingagents, but still can produce such foams; the provision of suchCFC-free, HCFC-free and HFC-free foams themselves; and the provision ofsuch foams suitable for use as a flotation foam in watercraft, as astructural foam or as an insulation foam.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, it has been discovered that analkyl alkanoate (or a derivative and/or precursor thereof) can be usedas a blowing agent without the need for any other organic blowing agentsto produce a rigid, closed-cell polyurethane foam having a free-risedensity of from about 1.3 lbs./ft.³ to about 4 lbs./ft.³ and exhibitinga shrinkage of less than 10% if the combination of polyols with whichthe isocyanate is mixed to produce the foam comprises a blend of polyolsin which at least 50% by weight is made up of at least onepolyalkoxylated amine polyol, polyalkoxylated ether polyol, or polyesterpolyol having a hydroxyl number of from about 150 to about 800. Thefoams so produced have been found to be surprisingly stabledimensionally and may be used in essentially any industry in which rigidfoams are employed, including uses as insulation in refrigerationsystems, as structural components and for floatation. This method may beused to produce all types of rigid foams derived from isocyanate,including rigid polyurethane, polyisocyanurate and modifiedpolyisocyanurate foams, such foams being referred to herein genericallyas polyurethane foams.

According to a two-component method of this invention in which acomponent A is mixed with a component B, component A comprises anisocyanate (such term includes mixtures and combinations of discreteisocyanates as is known in the art) and, preferably also a surfactant.The isocyanate may be any of the isocyanates conventionally used in theproduction of rigid foams. Thus, any of the polyfunctional isocyanates,such as diphenyl-methane-4,4-diisocyanate, xylylene diisocyanates,polymethylenepolyphenylisocyane, 3,3-diphenyldimethyl-methane-4,4-diisocyanate, 2,4-tolulenediisocyanate dimer, m-phenylenediisocyanate,tolulene diisocyanates, diphenyl-methane-2,4-diisocyanate, or mixturesthereof, may be used. Similarly, any conventional, A-side surfactant maybe incorporated into component A, if so desired. Examples of suchsurfactants include silicones, such as B8407 sold by GoldschmidtChemical Corp. or non-reactive polymers have been found to beparticularly suitable. Other compositions, such as a fire retardant,including those containing bromine, chlorine or phosphorus, may also beincluded in the component A.

In addition, component A may, but need not, contain blowing agent to beemployed in the foaming process. The blowing agent used is selected fromthe alkyl alkanoate family with methyl formate being the preferredblowing agent. It is also contemplated that a derivative and/orprecursor of the selected alkyl alkanoate may be used in place of someor all of the selected agent. Thus, when reference is made herein to“alkyl alkanoate” or any particular alkyl alkanoate and/or a “derivativeand/or precursor thereof” it should be understood that the alkylalkanoate itself is preferred, although one or more derivative and/orprecursor, or a combination of the alkyl alkanoate and one or morederivative and/or precursor may be employed. In addition, variouscombinations of two or more alkyl alkanoates or derivatives and/orprecursors thereof are specifically included herein.

By “derivative and/or precursor” of alkyl alkanoate, what is meant isany composition in which the alkyl alkanoate is attached to a carrier,such as a gas, that is inert with respect to the remaining ingredientsof components A and B. Thus, the derivative and/or precursor of thealkyl alkanoate maintains the functionality of the alkyl alkanoate.Preferably, if an alkyl alkanoate derivative and/or precursor is used,it is a complex that maintains the entire structure as a moiety of thecomplex. By “precursor”, what is meant is a composition that produces analkyl alkanoate at some point prior to or during the foaming process.

It will be understood by those of ordinary skill in the art that knownvariations of the formulations and teachings disclosed herein may benecessary to achieve desired characteristics of the finished foamdepending on the specific alkyl alkanoate, derivative and/or precursor,or combination thereof, selected as the blowing agent. These variationsare specifically included with the scope of the invention as claimed.

It is also possible for small amounts of other compositions that act asblowing agents to be present. For example, CFCs, HCFCs, HFCs, methylenechloride, fluorocarbons, hydro fluorocarbons, hydrocarbons or otherorganic compounds may be present that act as blowing agents. However, ifsuch compositions are present, they should total less than 20%,preferably less than 10%, more preferably less than about 5%, especiallyless than about 2%, of the total weight of blowing agents in componentA. Ideally, however, component A is free of such compositions.

The materials of component A may be blended in any standard manner. Theorder of blending is not particularly significant. Nevertheless, aconvenient order of mixing is to add surfactant to isocyanate, and thento add the acid inhibitor, if any, and finally to add the blowingagent(s), if any.

The relative proportions of ingredients should be such that if componentA contains one or more blowing agent, the concentration of blowingagent(s) in component A is from about 0.5% by weight to about 12% byweight, preferably about 2% by weight to about 10% by weight. The alkylalkanoate (and/or derivative and/or precursor thereof) itself may makeup as much as about 12% by weight, preferably as much as about 10% byweight, such as from about 2% by weight to about 10% by weight, ofcomponent A. The surfactant may make up less than about 2% by weight,preferably about 0.75% by weight, of component A. If an acid inhibitoris desired, it may be included in a concentration of up to about 0.5% byweight, based on the weight of component A. Typically, the balance ofcomponent A is the isocyanate.

As with component A, the ingredients of component B may be mixed in anyorder. Component B contains at least one polyol. The total of allpolyols in component B makes up from about 65% by weight to about 98% byweight, preferably about 86% by weight to about 92% by weight componentB. At least one of the polyol(s) in component B is a polyalkoxylatedamine, a polyalkoxylated ether or a polyester polyol and has a hydroxylnumber of from about 150 to about 800. Preferably, the hydroxyl numberis from about 300 to about 700, most preferably about 300 to about 500.The polyalkoxylated polyols preferably are alkoxylated with alkoxygroups of from two to about four carbon atoms; that is, they arepolyethoxylated, polypropoxylated, polybutoxylated or some combinationthereof. Those of ordinary skill in the art of rigid foam preparationwill readily recognize suitable polyols that correspond to each of thetypes of polyols described. By way of illustration and not limitation,however, the polyalkoxylated amine may be, for example, apolyalkoxylated aliphatic amine or a Mannich polyol, the polyalkoxylatedether may be, for example, a polyalkoxylated sucrose or glycerin, andthe polyester polyol may be a transesterification of a terephthalate orcastor oil. The polyols can be made individually or as coinitiators.

Component B may comprise one or more of the noted polyalkoxylated amine,one or more of the noted polyalkoxylated ether, one or more of the notedpolyester polyol, one or more of the noted polyalkoxylated amine incombination with one or more of the noted polyalkoxylated ether and/orone or more of the noted polyester polyol, or one or more of the notedpolyalkoxylated ether in combination with one or more of the notedpolyester polyol. In other words, one or more of any one of the threenoted classes of polyols, or any combination of polyols from any two orall three of the classes may be employed. Component B may comprise otherpolyols as well, especially those traditionally employed in rigid foams,but preferably, the total of all polyols present from the three classes(that is, the total of all polyols from any of the noted polyalkoxylatedamines, polyalkoxylated ethers and polyester polyols) make up more thanabout 50% by weight of all the polyols of component B, and at leastabout 50% by weight of component B.

It will be understood by those of ordinary skill in the art that theinvention encompasses formulations having lower levels of blowing agentand higher levels of amine polyol than are usually found in comparablefoams utilizing HCFC blowing agents. For example, a preferred formulashowing approximate percentages by weight of the ingredients for oneembodiment of the present invention is: Component A - Isocyanate  96.7%Surfactant  1.3% Methyl Formate  2.0% Component B - Polyalkoxylatedether  4.5% Polyalkoxylated ether 71.44% Polyalkoxylated amine  10.0%Surfactant  1.5% Catalyst 1  0.5% Catalyst 2  0.16% Catalyst 3  0.10%Diluent  5.0% Water  2.8% Methyl Formate  4.0%Such a formulation results in increased urea bonding which surprisinglyyields an increase in the dimensional stability of the finished foamdespite the use of the alkyl alkanoate blowing agent. It should beunderstood that other methods of increasing the urea or other polyolbonding, as are known in the art, are specifically included with thescope and teachings of this invention. Other advantages of theinvention, absent from the prior art, include avoiding or counteractingthe plasticizing effect of alkyl alkanoates on the cell structure of thefoam, eliminating the fluctuations experienced in the reactivity profiledue to catalyst instability, and raising the flash point of the reactionmixture to acceptable levels.

As will be readily understood by those of ordinary skill in the art ofproducing rigid foams upon reading this specification, the types andquantities of each polyol are determined by the ratio of alkyl alkanoateto water in the formula and the desired properties of the finished foam,and such ordinarily skilled artisan would recognize preferred quantitiesand ratios of polyols that would be preferred for a particularsituation, and how to adjust the quantities and ratios for coordinationand optimization for particular situations without undueexperimentation.

It also should be understood that the polyols in the combination neednot form a separate composition package to be added as a singleingredient to form component B. Thus, it is not necessary to mix thethree constituents of the mixture together to form a premix and then toform component B by mixing the premix with the remaining ingredients ofcomponent B, although that is an option. The ingredients of component Bmay be mixed in any order, and the polyols may be added separately fromeach other as separate ingredients to form component B.

Component B also comprises 0% to about 5% by weight, preferably fromabout 0.5% by weight to about 4% by weight, more preferably from about1% by weight to about 3% by weight, water. It is understood that thewater may serve not only as a blowing agent but also to add rigidity tothe resulting foam.

Component B further comprises an alkyl alkanoate, preferably, methylformate (and/or derivative and/or precursor thereof), as a blowingagent. The methyl formate (and/or derivative and/or precursor thereof)itself makes up as much as about 15% by weight, preferably from about 2%by weight to about 15% by weight, of component B.

Of course, the alkyl alkanoate (and/or derivative and/or precursorthereof) may be introduced by a separate stream in addition or in placeof that which may be in either or both of components A and B. Theconcentrations of alkyl alkanoate (or derivative and/or precursorthereof) in components A and B and the amount introduced to the reactionmixture by way of a separate stream are adjusted and coordinated so thatthe resulting concentration of total alkyl alkanoate (or derivativeand/or precursor thereof) brought together upon mixing components A andB and separate streams, if any, based on the total weight of theresulting mixture is from about 1% by weight to about 12%, preferablyfrom about 4% by weight to about 8%. Other blowing agents may beemployed or at least present, but it is preferred that the total amountof blowing agent(s) present in each component and in the totalcombination of all ingredients mixed together to form a foaming mixtureto be blown to form a rigid foam comprise less than 20% by weight,preferably less than 10%, more preferably less than about 5%, especiallyless than about 2%, by weight CFCs, HCFCs, HFCs fluorocarbons andhydrocarbons.

More preferably, however, the total amount of blowing agent(s) presentin each component and in the total combination of all ingredients mixedtogether to form a foaming mixture should be substantially free of (thatis, it should comprise less than 1% by weight) CFCs, HCFCs, HFCs,fluorocarbons and hydrocarbons. Even more preferably, the total amountof blowing agent(s) present in each component and in the totalcombination of all ingredients mixed together to form a foaming mixtureto be blown to form a rigid foam should be free of CFCs, HCFCs, HFCsfluorocarbons and hydrocarbons. It is especially desirable if the totalamount of blowing agent(s) present in each component and in the totalcombination of all ingredients mixed together to form a foaming mixtureto be blown to form a rigid foam is also substantially free of (that is,contains less than about 1% by weight) of any other substituted orunsubstituted hydrocarbon, and particularly free of any othersubstituted or unsubstituted hydrocarbons. Ideally, the total amount ofblowing agent(s) present in each component and in the total combinationof all ingredients mixed together to form a foaming mixture to be blownto form a rigid foam is substantially free of any other organic compoundthat acts as a blowing agent, optimally free of such organic compounds.When reference is made herein to “other” compounds such as “otherorganic compounds,” what is meant is compounds other than the alkylalkanoate and/or derivative and/or precursors thereof.

Component B may also contain other ingredients as desired. Those ofordinary skill in the art will readily recognize several types ofingredients known for use in rigid foam formulations and those may beemployed in the present invention as well. For example, a fire retardantsuch as those containing bromine, chlorine or phosphorus may beincorporated into the mixture to impart fire resistance. Other commonlyused additives are hydroxyl-containing compositions such as castor oil,aromatic polyesters, glycols and/or alkoxylated sorbitals, acidscavengers (for example, alpha-methyl styrene), acid formationinhibitors, catalyst stabilizers or diluents.

Component A and component B may be mixed, such as through a static mixchamber or any other such device commonly known in the industry, bystandard procedures to produce a homogenous blend. As with conventionalfoams, the isocyanate and the polyol(s) in the blend are allowed toreact together and to expand to form rigid foam. The method of thisinvention may be used to produce low density and standard density aswell as high-density foams. Component A and component B are mixed in arelative proportion such that the ratio of the cyano groups of componentA to the hydroxyl groups of component B, that is, the NCO/OH ratio orindex, is generally from about 0.8:1 to about 3:1. With respect topolyurethane foams, the weight ratio of Component A to Component B isgenerally within the range from about 150:100 to about 100:150,preferably to about 100:80-100:120. Polyisocyanurate foams may beproduced when the NCO/OH ratio is in the range of from about 2:1 toabout 3:1, such as about 2.5:1.

The rigid foam produced by the method of this invention has a low CFC,HCFC and HFC content and, if so desired, a low content of anyfluorocarbon or substituted or unsubstituted hydrocarbon other than analkyl alkanoate. In fact, if so desired, the foam may have a low levelof any organic compound other than the alkyl alkanoate. The foam mayeven be free of any such compositions. Yet, the foam still has a closedcell content of at least 85%, and typically well in excess of 85%.

Preferably the gas in the cells of foam, therefore, contain more than40% by weight CO₂ and alkyl alkanoate (and/or derivative and/orprecursors thereof), more preferably more than about 90% by weight,still more preferably more than about 95% by weight, even morepreferably more than about 98% by weight, and most preferably more thanabout 99% by weight or even about 100% by weight. In particular, becausethe method of this invention does not require any organic blowing agentin addition to the alkyl alkanoate, the level of other blowing agentsand gases in the foam may be set at any low level desired and even maybe eliminated entirely. Thus, by way of example, the gas in the cellsmay contain less than 20% by weight CFCs, HCFCs, and HFCs and, asdesired less than 10%, less than 5% or even less than 1 or 2% by weightCFCs, HCFCs, and HFCs. Likewise, the other substituted hydrocarbons oreven other organic compounds may be similarly limited. Although rigidfoams of free-rise density as high as 4 lb./ft.³ may be acceptable incertain uses, the foams of this method have densities even lower, suchas about 2.5 lb./ft.³ to about 4 lb./ft.³, preferably about 1.3 lb./ft.³to about 4 lb./ft.³, especially about 1.3 lb./ft.³ to about 2.5lb./ft.³.

Moreover, surprisingly, the foams of the present invention exhibitexcellent dimensional stability, easily sufficient to satisfy standardsrequiring less than 10% shrinkage by volume pursuant to the test methodsof ASTM-D2126. (When shrinkage is referred to herein, it refers to thevolumetric shrinkage pursuant to those test standards.) Thus, the foamsof this invention may be used in those applications that requirecompliance with 33 CFR § 183.114.

Dimensional stability and other desirable characteristics of the foamsof the present invention may enhanced further by packing the foam.During packing, a given amount of the foaming mixture, having a givenfree rise volume, is injected into a closed or substantially closedspace of a given volume. The percentage ratio by which the free risevolume of the foam exceeds the volume of the space into which it isinjected is termed the pack factor. Thus, if 2.0 pounds of foam have afree rise volume of 1.0 cubic foot, and 2.3 pounds of the foam isinjected into a closed or substantially closed space having a volume of1.0 cubic foot, the pack factor will be 115%.

Packing of the foam mixtures of the present invention results in adensification or thickening of the cell walls within the finished foam.The result is an even stronger, more stable cell and, therefor, finishedfoam. Moreover, such packing and thickening of the cell walls may helpslow the transfer of gases between the cells thereby increasing theeffective thermal energy efficiency of the finished foam.

A particularly surprising result of packing mixtures of the presentinvention is the substantial uniformity of cell size and densitydistribution gradient. Without being bound to any particular theory,applicants believe that these characteristics are the result of acombination of physical parameters including the improved flow of themixture and its higher boiling point.

Packing ratios of the present invention are from about 5% to about 50%,preferably from about 5% to about 25% and more preferably from about 10%to about 20%.

It is intended that the specification be considered exemplary only, withthe scope and spirit of the invention being indicated by the claimswhich follow. In view of the above, it will be seen that the severaladvantages of the invention are achieved and other advantageous resultsattained. As various changes could be made in the above methods andcompositions without departing from the scope of the invention, it isintended that all matter contained in the above description shall beinterpreted as illustrative and not in a limiting sense.

1. A method for producing rigid, closed-cell polyurethane foam having afree-rise density of from about 1.3 lbs/ft.³ to about 4 lbs/ft³ andexhibiting a shrinkage of less than 100%, comprising mixing together:(a) an isocyanate, (b) at least one polyol having a hydroxyl number offrom about 150 to about 800 and being selected from the group consistingof polyalkoxylated amines, polyalkoxylated ethers, and polyesterpolyols, wherein all of said at least one polyols make up from 50% byweight to 100% by weight of all polyols in the reaction mixture; and (c)at lea one blowing agent selected from the group consisting of methylformate, derivatives of methyl formate, precursors of methyl formate,and combinations thereof, wherein all of said at least one blowingagents make up more than about 80% by weight of all blowing agents inthe reaction mixture; to font a reaction mixture curable to produce thefoam.
 2. (canceled)
 3. A method as set forth in claim 1, furthercomprising the step of reacting the isocyanate and the at least onepolyol in the reaction mixture to produce the foam.
 4. A method as setforth in claim 3, wherein An at least one blowing agent is methylformate.
 5. A method as set forth in claim 4, wherein the methodcomprises mixing together (a), (b), (c) and water as a second blowingagent to form the reaction mixture.
 6. (canceled)
 7. A method as setforth in claim 4 wherein methyl formate makes up more than about 90% byweight of all blowing agents in the reaction mixture.
 8. A method as setforth in claim 7 wherein methyl formate makes up more than about 95% byweight of all blowing agents in the reaction mixture.
 9. (canceled) 10.A method as set forth in claim 5 wherein methyl formate and watertogether make up more than about 90% by weight of all blowing agents inthe reaction mixture.
 11. A method as set forth in claim 10 whereinmethyl formate and water together make up more than about 95% by weightof all blowing agents in the reaction mixture.
 12. A method as set forthin claim 11 wherein methyl formate and water together make up more thanabout 98% by weight of all blowing agents in the reaction mixture.
 13. Amethod as set forth in claim 5 wherein CFCs, HCFCs and HFCs togethermake up less than about 20% by weight of the blowing agents in thereaction mixture.
 14. A method as set forth in claim 13 wherein organiccompounds other than methyl formate make up less than about 20% byweight of the blowing agents in the reaction mixture.
 15. A method asset forth in claim 13 wherein organic compounds other than methylformate make up less than about 2% by weight of the blowing agents inthe reaction.
 16. A method as set forth in claim 14 wherein the reactionmixture is free of CFCs, HCFCs and HFCs.
 17. A method as set forth inclaim 16 wherein the reaction mixture is free of substituted andunsubstituted hydrocarbon blowing agents other than methyl formate. 18.A method as set forth in claim 16 wherein the reaction mixture is freeof organic blowing agents other than methyl formate.
 19. A method as setforth in claim 5 wherein the methyl formate and water are the onlyblowing agents in the reaction mixture.
 20. A reaction mixture curableto form a rigid, closed-cell polyurethane foam having a free-risedensity of from about 1.3 lbs/ft.³ to about 4 lbs/ft³ and exhibiting ashrinkage of less than 10%, comprising: (a) an isocyanate, (b) at leastone polyol having a hydroxyl number of from about 150 to about 800 andbeing selected from the group consisting of polyalkoxylated amines,polyalkoxylated ethers, and polyester polyols, wherein all of said atleast one polyols making up from 50% by weight to 100% by weight of allpolyols in the reaction mixture, and (c) at least one blowing agentselected from the group consisting of methyl formate, derivatives ofmethyl formate, precursors of methyl formate, and combinations thereof,wherein all of said at least one blowing agents make up more than about80% by weight of all blowing agents in the reaction mixture.
 21. Areaction mixture as set forth in claim 20 wherein the at least oneblowing agent is methyl formate.
 22. A reaction mixture as set forth inclaim 21, further comprising water as a second blowing agent. 23.(canceled)
 24. (canceled)
 25. A reaction mixture as set forth in claim20, consisting essentially of: (a) an isocyanate, (b) at least onepolyol having a hydroxyl number of from about 150 to about 800 and beingselected from the group consisting of polyalkoxylated amines,polyalkoxylated ethers, and polyester polyols, wherein all of said atleast one polyols make up from 50% to 100% by weight of all polyols inthe reaction mixture; (c) from 0% to about 50%11 by weight of at leastone other polyol, and (d) at least one blowing agent selected from thegroup consisting of methyl formate, derivatives of methyl formate,precursors of methyl formate, and combinations thereof, wherein all ofsaid at least one blowing agents make up more than about 80% by weightof all blowing agents in the reaction mixture.
 26. A reaction mixture asset forth in claim 25 wherein the blowing agent is methyl formate.
 27. Areaction mixture as set forth in claim 26, further comprising water thatacts as a second blowing agent.
 28. A rigid, closed-cell polyurethanefoam having a free-rise density of from about 1.3 lbs/ft³ to about 4lbs/ft.³ and exhibiting a shrinkage of less than 10%, produced by themethod of claim
 3. 29. (canceled)
 30. A foam as set forth in claim 29wherein the gas is free of CFCs, HCFCs, HFCs and hydrocarbons.
 31. Afoam as set fort in claim 28 wherein the foam is suitable for use as aflotation foam.
 32. A foam as set form in claim 28 wherein the foam issuitable for use as structural foam.
 33. A foam as set forth in claim 28wherein the foam is suitable for use as an insulation foam.
 34. Awatercraft comprising a foam as set forth in claim
 31. 35. A method forproducing a rigid, closed-cell polyurethane foam having a free-risedensity of from about 1.3 lbs/ft.³ to about 4 lbs/ft.³ and exhibiting ashrinkage of less than 10%, comprising mixing together: (a) anisocyanate, (b) at least one polyol having a hydroxyl number of fromabout 150 to about 800 and being selected from the group consisting ofpolyalkoxylated amines, polyalkoxylated ethers, and polyester polyols,wherein all of said at least one polyols make up from 50% by weight to100% by weight of all polyols in the reaction mixture; and (c) at leastone blowing agent selected from the group consisting of at least onealkyl alkanoate, derivatives of at least one alkyl alkanoate, precursorsof at least one alkyl alkanoate, and combinations thereof wherein all ofsaid at least one blowing agents make up more than about 80% by weightof all blowing agents in the reaction mixture; to form a reactionmixture curable to produce the foam.
 36. A reaction mixture curable toform a rigid, closed-cell polyurethane foam having a free-rise densityof from about 1.3 lbs/ft.³ to about 4 lbs/ft.³ and exhibiting ashrinkage of less than 10%, comprising: (a) an isocyanate, (b) at leastone polyol having a hydroxyl number of from about 150 to about 800 andbeing selected from the group consisting of polyalkoxylated amines,polyalkoxylated ethers, and polyester polyols, the at least one polyolmaking up from 50% by weight to 100% by weight of all polyols in thereaction mixture, and (c) at least one blowing agent selected from thegroup consisting of at least one alkyl alkanoate, derivatives of at lastone alkyl alkanoate, precursors of at least one alkyl alkanoate, andcombinations thereof wherein all of said at least one blowing agentsmake up more than about 80% by weight of all blowing agents in thereaction mixture.
 37. A rigid, closed-cell polyurethane foam having afree-rise density of from about 1.3 lbs/ft.³ to about 4 lbs/ft.³ andexhibiting a shrinkage of less then 10%, comprising cells containinggas, at least about 80% by weight of the gas being at least onealkanoate and carbon dioxide.
 38. The method of claim 35 furthercomprising the step of packing of the reaction mixture at a packingratio of about 5% to about 50%.
 39. The foam of claim 37 wherein saidfoam has been packed to a packing ratio of about 5% to about 5%.
 40. Areaction mixture of claim 36 wherein said mixture comprises an A-sideand a B-side having substantially the following general formulationapproximate percentages by weight: Component A - Isocyanate  96.7%Surfactant  1.3% Methyl Formate  2.0% Component B - Polyalkoxylatedether  4.5% Polyalkoxylated ether 71.44% Polyalkoxylated amine  10.0%Surfactant  1.5% Catalyst 1  0.5% Catalyst 2  0.16% Catalyst 3  0.10%Diluent  5.0% Water  2.8% Methyl Formate  4.0%